NAIROBI -- The U.N. peacekeeping mission in Congo is collaborating with known human rights abusers as it backs a brutal Congolese military operation that has led to the deliberate killing of at least 1,400 civilians and a massive surge in rapes, according to a report by Human Rights Watch.

The 183-page report, the fullest accounting so far of the operation, is a chronicle of horrors. It describes gang rapes, massacres, village burnings and civilians being tied together before their throats are slit -- many incidents carried out by a Congolese army being fed, transported and otherwise supported by the United Nations.

The report calls for the U.N. peacekeeping mission to "immediately cease all support" to the Congolese army until the army removes commanders with known records of human rights abuses and otherwise ensures the operation complies with international humanitarian laws.

"Continued killing and rape by all sides in eastern Congo shows that the U.N. Security Council needs a new approach to protect civilians," said Anneke Van Woudenberg, a senior researcher with Human Rights Watch.

The Security Council is scheduled to meet this week to discuss the Congolese peacekeeping mission's mandate, which is the United Nations' largest and most expensive. A mission spokesman said officials are studying the report and declined to comment. The United States also has a small military team in Congo assisting the Congolese army.

The Congolese military operations, which began in January, were intended to root out abusive Rwandan rebels who have lived mostly by force among eastern Congolese villagers for years, fueling a long-running conflict that has become the deadliest since World War II.

The rebels -- known as the Democratic Forces for the Liberation of Rwanda, or FDLR -- include some leaders accused of participating in the 1994 genocide in neighboring Rwanda. The initial phase of the military operations were backed by Rwandan troops.

But as the Rwandans departed in February, U.N. peacekeepers stepped in, supplying attack helicopters, trucks, food and other logistical support to a Congolese army known as one of the most abusive militaries in the world. At the time, the head of the U.N. mission, Alan Doss, said that the operations were necessary and that some civilian casualties were inevitable.

But the Human Rights Watch report does not document the story of civilians accidentally caught in the crossfire. Instead, it details a chilling pattern of deliberate civilian killings by Congolese and Rwandan soldiers and the rebels they are fighting. Both sides, the report says, have carried out a strategy of "punishing" villagers they accuse of supporting the wrong side.

To that end, the report says, Congolese soldiers and their Rwandan allies did not simply shoot their victims but beat them to death with clubs, stabbed them to death with bayonets or chopped them into pieces with machetes, making a pile of body parts for other villagers to see.

In one village, the soldiers called women and children to a school for a meeting and then systematically began killing them, the report says. In another case, a woman said she watched as soldiers beat six members of her family to death with wooden clubs. Four soldiers then accused her of being a rebel wife and gang-raped her. In general, the report found, rape cases skyrocketed in areas where Congolese soldiers were deployed.

The report documents a similarly ruthless pattern of retaliation by the FDLR, which killed with machetes and hoes, accusing villagers of betraying them. The rebels often targeted village chiefs or other influential people to frighten the wider population, the report says. They gang-raped women, frequently telling their victims they were being punished for welcoming the Congolese army.

In all, the report's authors documented more than 1,400 killings, roughly half by the Congolese army and their Rwandan allies and half by rebels. It said more than 900,000 people have been forced to flee their homes since January, the sort of massive displacement that has led to an estimated 5 million deaths from hunger and disease since eastern Congo's conflict began about 15 years ago.